Conventionally, when forming a 2-dimensional code by laser marking, a marking pattern has been formed by applying a laser beam to a black cell (a portion with a code color) and not applying the laser beam to a white cell (portion with a background color) constructing a code symbol of 2-dimensional code.
As described above, when the laser beam is applied, a portion where the laser beam is applied generates a color and a portion where the laser is not applied remains a material's color, which generates a contrast of bright and dark between the color generated portion and the material's color remained portion. In this way, 2-dimensional code has been formed by a marking pattern having a bright/dark portions consisting of the colored cells and the cells having the material's color on a surface of a material.
In addition, when reading the 2-dimensional code generated by laser marking, a pattern having a bright/dark contrast consisting of the colored cells and the cells having the material's color has conventionally been taken in using CCD cameras or laser scanners and made a reading device recognized as an image data.
In such a method for generating 2-dimensional code, when a portion where the laser beam is applied expresses a darker color than a color where the laser beam is not applied, that is, the material's color, a portion assumed as the cell having a dark color in a code symbol of 2-dimensional code of original image becomes a dark mark even in a marking pattern formed on the surface of material.
That is, as shown in FIG. 8(B), on a material on which a portion where the laser beam is applied, that is, a marking portion by laser marking expresses a dark mark, 2-dimensional code just like an original image in which the code portion expresses a dark mark as shown in FIG. 9(A) is formed.
On the other hand, depending on materials on which a marking is executed, such a case that a portion where the laser beam is applied expresses a brighter color than the material's color may occur. For example, when Aluminum material is laser marked, a portion where the laser beam is applied generates a white color resulting in generation of bright mark. In general, in such materials as a transparent material such as glass, metal, resin, cloth, ceramics and silicon, a marked portion generates a bright color.
That is, as shown in FIG. 8(C), on a material on which a marking portion expresses a bright mark, a bright/dark-reversed image in which the code portion expresses a bright mark as shown in FIG. 9(B), that is, a reversed 2-dimensional code is formed.
In this way, when 2-dimensional code is formed by laser marking, a bright/dark-reversed 2-dimensional code may be formed depending on kind of material to be marked. Thus, in the reading device for reading the laser marked 2-dimensional code have been equipped with bright/dark reversing function.
In such reading device, it is general to read 2-dimensional code with a mutual conversion method in which, after taking-in an image data of bright/dark reversed 2-dimensional code, a color of a portion recognized as a dark mark (material's color to be marked) is converted to a bright color to recognize it, and at the same time, a color of a portion recognized as a bright mark (a portion where white color is generated by laser beam application) is converted to a dark color to recognize it.
In contrast, as a method for forming a barcode by printing, a barcode printing is known that is possible to print a barcode that can be correctly read out the pattern even if the barcode has been generated as a combination of a white system printer ribbon and a black system background (for example, refer to FIG. 1 of page-2 and FIG. 21 of page-7 in Patent Gazette “Tokukaihei 7-125312”).
A barcode printer described in the Patent Gazette “Tokukaihei 7-125312” is equipped with a data conversion means that converts a dot pattern data for printing the barcode to a black/white reversed dot pattern data for printing the reversed barcode. This data conversion means executes data conversion of dot pattern data for printing when an ink color is white system and a background color is dark system based on colors of printer ribbon and background detected by a color recognition means. Thereby, it is comprised so as to be possible to accurately print the not-reversed barcode at any time.
However, in 2-dimensional code formation technology by laser marking, it has not been executed to form always the non-reversed 2-dimensional code against the marked materials of any kind by executing a bright/dark conversion of 2-dimensional code's marking data corresponding to the marked materials. Instead, as described above, it has been possible to correctly read out the 2-dimensional code similarly to ordinary 2-dimensional code even if it is a bright/dark revered code by adding a bright/dark reversing function mostly to the reading device side.
Further, when it is required to use either an ordinary reading device or a reading device equipped with bright/dark reversing function depending on the type of material, there have been a problem of lack of convenience. In addition, if it is always required to use the highly functional reading device equipped with bright/dark reversing function, there has been a problem of cost increase.
In general, it is necessary to keep a margin of space with a predetermined dimension around a code symbol of 2-dimensional code. Such margin is called as a “quiet zone”. Required size of this margin changes depending on code. For example, in case of QR code, a margin of width corresponding to four cells is required.
When non-reversed 2-dimensional code is formed by laser marking, and an area with a body color or bright color area is reserved around the 2-dimensional code, this bright color area becomes a quiet zone. But, when bright/dark reversed 2-dimensional code is formed, a body color area surrounding this 2-dimensional code becomes a code color (dark color) area. That is, no quiet zone is formed around the bright/dark reversed 2-dimensional code. Thus, in case of bright/dark reversed 2-dimensional code, there has been such a problem that boundary of area in which 2-dimensional code has been marked is hard to be accurately recognized and it becomes impossible to execute reading the 2-dimensional code.
Furthermore, when executing laser marking against a transparent material such as glass or liquid crystal, for example, in general, a portion where laser beam is applied generates white color and becomes a bright mark and a portion where a transparent body is remained as it is becomes a dark portion to form a bright/dark reversed 2-dimensional code. However, a body color of transparent material is recognized differently affected by some objects or light source located at behind the transparent material. Therefore, for example, when the object behind the transparent material is something white, contrast between the color generated portion by laser beam and the body portion where laser beam is not applied becomes small, thereby the boundary of this portion becomes hard to be recognized when 2-dimensional code is taken in as an image data by CCD camera or laser scanner, etc.
That is, when executing laser marking against the transparent material and if the transparent material is located on bright background, a marking pattern becomes unclear and the area in which 2-dimensional code is marked becomes unclear. Thus, such a problem that read out of 2-dimensional code becomes impossible occurs. In order to enable to read out surely the 2-dimensional code, it has been required to make the boundary of area in which 2-dimensional code exists clear.
In view of the above described problems, the objective of this invention is to provide a method for generating 2-dimensional code by laser marking and a laser marking device that is possible to form a non-reversed 2-dimensional code.
Another objective of this invention is to provide a method for forming 2-dimensional code by laser marking and a laser marking device that is possible to surely read out the 2-dimensional code by making the boundary of laser marked 2-dimensional code's area clear.